This invention relates to phase shifting mechanisms and particularly to a phase shifting mechanism for projected fringe contouring devices.
Surface profile measuring by means of non-contact optical methods are widely used in a variety of fields including medicine and human modeling applications.
U.S. Pat. No. 4,984,893 issued to Steven R. Lange on Jan. 15, 1991 and entitled "Phase Shifting Device and Method" discloses a phase shifting device for producing transverse shifts of a projected grating. In that patent, the phase shift is accomplished by use of a flat transparent glass plate which is rotatable about an axis generally parallel to the lines of the grating. The transparent glass plate is rotated through a plurality of selected angles to provide modulation of the phase of the grating projected on the test surface.
While the device disclosed in that patent accomplishes its intended purpose, it is relatively costly as it requires the use of an expensive step motor and related controller to rotate the lens. In addition, the time necessary for the motor to rotate between the desired angles is substantial and increases the time necessary to complete each cycle of the imaging process.